The present invention relates to hydraulic systems, more particularly, to hydraulic systems which utilize discrete volumes of hydraulic fluid to perform work on a workpiece located remote from the main hydraulic unit of the hydraulic system, the main hydraulic unit being in fluid communication with the workpiece via hydraulic fluid lines.
Hydraulic systems which include a workpiece located remote from the main hydraulic unit utilize hydraulic lines to maintain fluid communication with the workpiece. In some instances, it is possible to experience a total draining of hydraulic fluid from the fluid reservoir associated with a hydraulic system as a result of hydraulic line failure (line rupture or fracture) or a failure in the workpiece. By way of illustration, the conventional vehicle hydraulic braking system contains a common hydraulic fluid reservoir which supplies fluid to a master brake cylinder or main brake valve in fluid communication with the individual brake subsystems via brake lines. Should a brake line fail or the brake actuator associated with a brake subsystem develop a leak, a means is provided through which hydraulic fluid can escape from the brake system fluid reservoir which may result in a total loss of vehicle braking capacity. Control valves have been employed in vehicle braking systems to protect the fluid reservoir should a brake line or brake actuator failure occur, in furtherance of operational integrity between the forward and rear brakes of a vehicle, i.e., a failure in either of the forward or rear brake will not deprive the housing vehicle of all braking capacity.
The control valve, in response to a fluid pressure differential resulting from a failure of either the forward or rear brakes or brake lines obstructs hydraulic fluid passage to the failed brake subsystem, either forward or rear, while allowing the remaining brake subsystems to properly function, and in so doing protects the hydraulic fluid reservoir associated with the vehicle braking system from rapid depletion.
It is sometimes desirous to maintain operational integrity and protect against fluid loss between complementing brakes, i.e., the brakes on either of a vehicle in the front or rear. For example, a crawler tractor is steered by varying the braking action between the right and left drive tracks, and many farm tractors have the ability to vary the braking action between the right and left rear wheels to achieve enhanced maneuverability. The inclusion of a conventional control valve to further integrity between complementary brakes, has displayed undesirable effects on vehicle maneuverability, in that, it has been observed that prior full actuation of either the right side brake or left side brake has resulted in the complementing brake being subsequently unengageable, which represents an unsafe condition. The undesirable effects appear to be the result of a pressure differential experienced by a contained piston of the main control valve created during the prior full actuation of the brake on one side of the vehicle.
Flow restricting orifices have been used in place of control valves to assist in creating integrity between complementing brakes. However, a flow restricting orifice only reduces the rate of fluid lost due to a failure; an orifice cannot stop the loss of fluid.
The present invention prevents appreciable hydraulic fluid volume losses from a hydraulic system, wherein discrete volumes of hydraulic fluid perform work on the remotely located workpiece, fluid losses facilitated as a result of the failure of a remotely located workpiece or a failure in a hydraulic line communicating the workpiece with the main unit of the hydraulic system.